The invention relates in general to processes and apparatus for providing a laminar flow of inert fluid effectively around a molten and cooling weld puddle and in particular to processes and apparatus for providing a laminar flow of inert fluid in the form of a leading and/or trailing shield to protect a molten and cooling weld puddle during the welding operation.
Generally, welding involves application of the heat generated by a welding torch to a work piece, or to a joint between adjacent metal parts in a localized manner to effect fusion between the pieces or parts to be joined. Such a welding operation usually takes place in the presence of an inert shielding gas to prevent contamination of the region being treated, such as a molten weld puddle, from the surrounding air. Commonly, the inert shielding gas is introduced to a molten weld puddle area via an annular passageway or other passageways surrounding a welding torch to protect a very limited area beneath the torch from the surrounding air. Shielding a very limited area in this manner, however, can adversely affect, inter alia, the mechanical and corrosion resistance properties and the surface appearance of a weld. Weld areas, for example, can still be subject to air contamination or oxidation during the welding stage when an inert gas is contaminated with the surrounding air or during the solidification stage when an inert shielding gas is no longer present.
Due to the recognition of the importance of a shielding means in obtaining high quality weld areas, various shielding arrangements have been Proposed. For instance, U.S. Pat. Nos. 4,166,940, 4,179,059, 4,528,436 and 4,567,343 show a double shielding means wherein an initial shielding means is augmented or supplemented with a secondary shielding means. Inert shielding gases are introduced in such a manner as to provide the initial shielding means generally surrounded with the secondary shielding means. Similarly, U.S. Pat. No. 4,839,489 shows a plurality of shielding means wherein inert gases are provided in a trailing and leading fashion to protect the freshly welded area and an area ahead of the welding torch which is preheated due to close proximity to the welding operation. These shields, however, may not be effective in protecting the welded area from the surrounding air as the air migrates or aspirates into the heated region. The failure to reduce turbulence, which may result from a high welding speed, around an area to be welded or to maintain a proper flow of inert fluid, for example, may cause oxygen entrainment in the welded area or oxidation of the welded area. The effectiveness of these shielding means can further deteriorate as the flow of an inert shielding gas is hindered or hampered as a result of condensing metal vapors clogging the porous diffusing surface of a diffuser. Moreover, molten weld materials, which may propel away from a weld area during the welding operation, may cause damage to a welding system involved or cause an injury to a person operating the welding system.
It is an advantage of the present invention in providing an improved shielding arrangement wherein the quality of the finished weld is enhanced; thus reducing the need for postweld cleaning and improving the quality of postweld plating which may be applied to the finished weld.
It is another advantage of the present invention in recognizing a better method for obtaining a laminar flow of inert fluid around a molten and cooling weld puddle during the welding operation.
It is yet another advantage of the present invention in increasing a welding speed while minimizing oxidation of the bead surface, i.e. the weld area.
It is a further advantage of the present invention in mitigating or alleviating the clogging effect on the porous surface of a diffuser, thereby preventing any interference in the flow of a shielding fluid.
It is an additional advantage of the present invention in providing a means by which the weld spatter can be prevented from damaging the welding apparatus involved.